On Wed, Feb 03, 2021 at 02:55:37PM -0800, Yu-cheng Yu wrote:

When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
a writable vma.  A shadow stack vma is writable, but its PTEs need
_PAGE_DIRTY to be set to become writable.  For this reason, maybe_mkwrite()
has been updated.

There are a few places that call pte_mkwrite() directly, but effect the
same result as from maybe_mkwrite().  These sites need to be updated for
shadow stack as well.  Thus, change them to maybe_mkwrite():

- do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
  and call pte_mkwrite(), which is the same as maybe_mkwrite().  Change
  them to maybe_mkwrite().

- In do_numa_page(), if the numa entry 'was-writable', then pte_mkwrite()
  is called directly.  Fix it by doing maybe_mkwrite().

- In change_pte_range(), pte_mkwrite() is called directly.  Replace it with
  maybe_mkwrite().

  A shadow stack vma is writable but has different vma
flags, and handled accordingly in maybe_mkwrite().

Signed-off-by: Yu-cheng Yu <redacted>

Reviewed-by: Kees Cook <redacted>

-- 
Kees Cook